Monoblock lasers, which typically include a number of optical elements assembled on a common substrate to provide a compact, single-piece laser, are used in a variety of applications. For example, monoblock lasers are typically used in laser rangefinders and targeting systems and have proven to be rugged, thermally reliable, and cost effective to produce.
A conventional monoblock laser (e.g., eye-safe, monoblock laser resonators) may include a Nd:YAG gain block, a Cr4+:YAG passive Q-switch, and a KTP nonlinear frequency-conversion crystal (e.g., all of square cross-section), which are permanently bonded (along with other optical components as required by the desired application) in precise, optical alignment to an undoped YAG rail or other type of common substrate to provide a stable, unified structure. The KTP crystal requires linearly polarized laser radiation for frequency-conversion and therefore some method for polarizing the resonant radiation must be provided.
The conventional approach for achieving polarization is by providing the Nd:YAG gain block with an internal Brewster interface, but this approach has a number of disadvantages. For example, the Nd:YAG gain block must be fabricated as two separate sub-blocks having precisely matched, Brewster-angled optical faces, which requires special fixtures and additional processing time to manufacture this Brewster pair to the required optical tolerances. The resulting Brewster pair is substantially longer than otherwise necessary for efficient laser operation and the assembled interface is difficult (or impossible) to clean when necessary. Furthermore, the Brewster “toes” are very fragile and breakage contributes to reduced yield at all stages of manufacture and the Brewster interface may contribute to additional resonator loss and beam quality degradation. Thus, substantial savings in time and cost may result along with potentially increased performance if the Brewster interface can be eliminated.
Other conventional polarization methods, as an alternative to the Brewster interface within the Nd:YAG gain block, may include cube polarizers (e.g., too expensive), thin parallel plates oriented at the Brewster's angle (e.g., too fragile), or a self-polarizing laser medium such as Nd:YVO4 (e.g., less reliable than Nd:YAG). However as indicated, these approaches also have certain undesirable limitations. As a result, there is a need for improved monoblock laser techniques that, for example, may improve performance and may provide an inexpensive and reliable alternative to the Brewster interface without adding unnecessary complexity.